Fig. 17

Sequential change of 15-1 crater. a Soon after the eruption, a mud pool formed in the bottom of the crater and vigorous fountaining of mud (arrow) was observed. b A sudden and transient explosion at 15-1 crater on 12:01 of July 21, 2015. c Boiling mud pool formed within 15-1 crater. d Fumaroles formed after a landslide that took place in August 2016